Transmission lines are used in a myriad of applications from within small handheld electronics transferring communication signals to large power systems transferring large amounts of power. In its simplest form, a transmission line is merely a conductor of electricity from one point (a source) to another (load). Transmission lines may be used for alternating current or direct current where deleterious alternating current surges differing from the fundamental frequency generated by the source may be induced to exist. The elements of the transmission line that allow development of such deleterious surges are the inductance, capacitance, and resistance inherent in the physical characteristics of the transmission line. These physical characteristics allow modes of the frequency components in the surges to induce reactances whose vector sums with the resistance of the transmission line result in an impedance upon which the voltage and current surges are developed. Voltage surges can break down insulation in the system, incapacitating a system by creating electrical shorts. Current surges also incapacitate a system by destroying control elements; switches, fuses, transistors, diodes, etc.
Ideally, transmission lines transfer signals without loss and without alteration of signal information content. If the transmission line characteristics are not optimized for the system, the received signals may be significantly altered, even over relatively short distances. Worse, even when, the transmission line characteristics are optimized, they may allow damaging resonances to form within the transmission line resulting in the aforementioned surges of line current and/or voltage.
For example, the Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTMS) at INL (Idaho National Laboratory) uses a coaxial style of transmission line to carry swept high-frequency power (50 Hz to 4 MHz) to metal plates of an ion cyclotron resonance (ICR) cell within a high vacuum and within the strong (7-Tesla) field of a superconducting magnet. This transmission line is severely constrained by two phenomena. First, if the transmission line has too little line capacitance (less than 60 pf), damaging resonances can occur at high frequencies within the transmission line resulting in reflected voltage surges which can puncture the metal-oxide-semiconductor gate structures of FETs (field-effect-transistors) used in the FTMS. Second, if the transmission line has too much capacitance (greater than 100 pf), the current demanded by the combined transmission line and load capacitance exceeds the current limit of the FETs resulting in their destruction.
Another example is the use of stepper motors to control the position of weldments and/or welding torches in a remote, high radiation field, automated process such as that designed for use in Yucca Mountain. State-of-the-art welding systems cannot currently extend beyond approximately 100 feet from their controllers due to the build-up of damaging resonances resulting in the breakdown of insulation in the motors and transmission lines. The need to maintain and operate the controllers in a minimal radiation field for protection of their operators begs for a solution to allow extending the cable length.
Various methods are used to adjust the line reactance (combination of capacitance, inductance, and resistivity) of a transmission line. Obviously, the length or diameter of the wire or the type of insulating material used in a transmission line may be altered to adjust capacitance of the transmission line. Unfortunately, in many instances, these may not be readily changeable or may already be optimized.
Various components may also be added to a transmission line such as capacitors and/or inductors to form filters which seek to control the allowable modes of the frequency components thereby minimizing potential surges. Unfortunately, when capacitors or inductors are used, they act as voltage dividers reducing the voltage transmitted through the transmission line.
Therefore, there exists a need for a device and method for altering the effects of reactive components of a transmission line without substantially altering the transmission line's physical characteristics or reducing the strength of the signal transmitted.